This invention relates to a dental pin assembly which comprises a dental pin for anchoring dental superstructures e.g. caps, veneers, onto a tooth, and a dental pin holder to facilitate the handling of the dental pin by the dental surgeon.
In particular, the present invention relates to dental pin assemblies in which the dental pin is a threaded pin and is for self-tapping insertion into the dentine of the tooth. Such pins commonly have a threaded portion which is releasably connected to a shank portion through a low shear neck portion. The threaded portion of the pin is inserted into the dentine to a pre-determined level at which a resistance to rotation is established, and any rotation against this resistance then provides sufficient torque to shear the pin at the neck portion. Shearing of the neck portion leaves a portion of the pin projecting from the surface of the dentine to which a dental superstructure can be secured.
Prior art threaded pins have had their threaded portions formed by precision machining, with further machining to provide the low shear neck portion. A significant disadvantage with machining to form the threaded portion of the pin is that a large amount of raw material is wasted, and since the materials used to make dental pins tend to be very expensive the cost of manufacturing pins by this process is very high.
The small dimensions of dental pins necessitate the use of a dental pin holder to facilitate handling and fitting of the pin into the dentine of the tooth. These holders typically comprise a cylindrical body which has a longitudinal central bore into which the shank of the dental pin is slid and subsequently secured therein. The central bore can be open at both ends or closed at one end depending upon type of method used to secure the shank within the bore.
The shank can be releasably or permanently secured within the bore, but permanent securement is preferred since releasable attachments used in the past have proved to come undone during fitting of the dental pin. A wide variety of methods for permanently securing the shank of the dental pin within the bore of the dental holder are known, examples of which are described in GB 1482681, EP 179599 and EP 56198.
The holder can be part of a standard dental hand-piece to be used manually by the dental surgeon, or more commonly the holder is for releasable attachment to an automated device capable of rotating the entire dental pin assembly.
Once the dental pin has been sheared at the neck portion as described above, both the shank and the holder are disposed of. It is therefore desirable that the holder be made of a relatively cheap material, and that the volume of the shank is as small as possible to reduce the ultimate cost of the dental pin assembly as a whole.